This invention relates to a phenolic resin composition for making a binder for mineral wool insulation products. Typically, phenol formaldehyde resoles (PF) used in binders for wool insulation products have large amounts of free formaldehyde. This is due to the high molar ratio between formaldehyde and phenol typically used for insulation resins. Various techniques have been used to reduce formaldehyde in the resin, such as the use of formaldehyde scavengers. One of these techniques employs using urea. Urea reduces formaldehyde emission, improves the anti-punk property of the binder, and reduces binder cost. However, the addition of urea makes the mixture unstable during storage. Precipitation of higher molecular weight components such as tetradimers and dimethylol urea (DMU) is a problem that results from employing urea. Therefore, this mixture generally must be used within a short period of time. Generally, urea is added to the resin as a 50% solution. It is allowed to react with the formaldehyde for 3-8 hours. The length of reaction time varies depending on the rate of binder usage, and this causes process variations. Long reaction times normally produce precipitation of tetradimers and DMU. This is due to the reduction of free and available formaldehyde as it reacts with urea. Because formaldehyde is a solvent, a reduction of free formaldehyde down to 1% or less will result in the precipitation of tetradimers as well as DMU. Precipitation causes plugged nozzles and blinding of conveyor belts, which will result in downtime and reduced process efficiency.
Several methods have been used in the industry to minimize precipitation of tetradimers and DMUs but these have been of limited use because of various drawbacks. In the present invention, it is discovered that a small amount of sodium tetraborate added during the PF resin cook produces a remarkably stable neat resin and its pre-react.